A commonplace substitution for the traditional wooden doors in residential and commercial buildings is a door made from steel or fiberglass. One type of synthetic door is formed with resin sheets reinforced with fiber glass (in the art referred to as door skins) attached to opposite sides of rails and stiles forming a rectangular frame, with the resulting cavity between the door skins filled with a polymer foam material. Doors so constructed can include wood graining on the outer surfaces of the skins, and also raised paneling formed (molded) in the skins, which gives these doors the appearance of natural wood fabricated products.
Molded skins for making such doors are typically formed using mixtures having by weight 12% to 15% polyester resin, 5% to 15% polystyrene, 40% to 50% calcium carbonate and 15% to 25% chopped fiberglass. Such mixtures are deposited in a compression molding machine and subjected to pressures from 600 to 1,500 psi and elevated temperatures for a cure cycle of from 60 to 200 seconds to form rigid skins. The mixture described is one of those known as a “sheet molding compound” (SMC).
The door skins formed from SMC processes for doors can have thicknesses of from about 0.13 mm (0.05 inches) to about 52 mm (0.20 inches), depending on the door application in which they are used.
As previously noted such skins are affixed to opposite sides of a rectangular frame and the core (cavity) enclosed by the frame and skins is filled with polymer foam to complete the door. A rigid urethane foam having a density of 0.8 pounds per cubic foot to 3.5 pounds per cubic foot is suitable for the core of such doors.
Previously, these doors may have had glass inserts (glazing or lights) that covered less than 30% of the door's exterior surface. Currently the marketplace demands doors with larger glass inserts, which can comprise more than 60% of the door's exterior surface. Due to building codes, these large glass inserts must be double glazed (double pane) and in some cases made of safety glass. While known doors with glass inserts have proven to be acceptable for various applications, such doors are nevertheless susceptible to improvements that may enhance their performance and lower cost. With this in mind, a need exists to develop improved doors with glass inserts that advance the art.